Surgeons are generally dexterous and highly trained to achieve a standardized level of surgical skill. However, surgeons have limitations, including a lack of micron-level geometric accuracy. For example, a surgeon cannot place an instrument at an exact, numerically defined location (within, say, 100 μm) relative to a patient's body part and then move the instrument through a defined trajectory. Many surgeons are unable to exert a precise, predefined force in a selected direction. Furthermore, a surgeon may have small hand tremors that limit his/her ability to operate on very small and delicate structures. Unfortunately, many of these limitations affect the outcome of certain surgical procedures, especially in cases where micron-level geometric accuracy is required. For example, the three-dimensional locations and directions of basic procedures used to modify a bone (including drilling, cutting, and reaming) determine the alignment and fit of the implant(s). These factors directly influence these functional outcomes.
Recently, to assist surgeons in overcoming these limitations, computer-assisted surgery (CAS) utilizing robotic- or image-guided technologies has been introduced into various medical fields. CAS, as a categorization or surgical technology, includes not only robotics but also image-guided surgical devices, surgical navigation systems, pre-operative planners, and surgical simulators.
A primary goal of CAS technologies is to integrate pre-operative planning with intra-operative performance. One of the most important steps in integrating pre-operative medical images directly into operating room procedures is registration of image and corresponding body part(s). Registration is a computational procedure that matches pre-operative images or planning information to the position of the patient on the operating room table. Rigid pins or other fiducial markers were used in early systems, such as in a robot-assisted system.
For robot-assisted total knee alignment (TKA) surgery, illustrated in FIG. 1, two spaced apart pins, 11A and 11B, are fixed to a target bone 12 before CT images are formed of the damaged bone region 14. The phrase “CT imaging” or “CT scanning” will refer herein to any suitable two- or three-dimensional imaging procedure, including computer tomography, and magnetic resonance imaging. The pins, 11A and 11B, are used to allow alignment of a three-dimensional (3-D) reconstruction of the patient bone 12. The intra-operative locations of the pins are used to relate the position of the patient's bone to a pre-operative plan, using a robot controller 14.
Based upon a converted CT scan image of the exposed bone(s) in the damaged bone region, the location and angular orientation of the femoral mechanical axis (FMA), femoral anatomical axis (FAA) and tibial mechanical axis (TMA) are also determined, and a pre-operative plan for orientation and movement of the milling machine 16 are determined in a coordinate system relative to the target bone 12, to mill the bone end according to a pre-programmed cutting file. After the registration process i.e., matching the CT image bone model with the target bone using the two pins, the robot assistant is activated, and the milling cutter attached to a robot arm mills the damaged bone region to create one (or preferably several) exposed planar surfaces (transverse, anterior, chamfer, etc.) to accept and mate with a femoral implant.
This method is accurate, to the extent that the ready-made implant device matches the patient's own bone surfaces, but requires at least two surgical operations (including incisions or cutting for each): a first operation for installation of a robotic calibration mechanism and a second operation for the final surgery to install the TKA device itself.
The second surgical operation is constrained by a tourniquet time limitation, which places a practical limit on a maximum cumulative time an open wound can be exposed (usually 90-120 min for TKA) without severe danger of infection. This is another disadvantage of robot-assisted surgery, which requires use of a registration process and of a bone location fixation process, both time consuming. As compared to robot-assisted surgery, a conventional manual TKA procedure is usually completed in no more than 30 minutes, despite a relatively high probability of misalignment.
Shape-based registration, illustrated in FIG. 2, is an alternative method as shown in the previous art for TKA and THA that has been developed recently and currently used in clinical trials. A patent's damaged bone 21D is exposed, in a first surgical operation. A location coordinate sensor 22 is placed in contact with the damaged bone surface 21 at each of a a selected sequence of spaced apart locations, and the coordinates of each such surface point are received by a location coordinate processor 23 for subsequent processing. The processor 23 provides an approximate equation for the surface of the damaged bone region 21D. At least 15 surface coordinate triples are selected and digitized on the actual bone surface, and the data are analyzed and processed to match, as closely as practicable, the CT scan image data, using interpolation, extrapolation and other suitable mathematical approximations. When a matching relation is found, optical or other sensors track and guide a tracking device to provide a surgeon with the location and angular orientation information needed to identify a suitable implant device. For a TKA procedure, the image formation system guides and locates the tracking device to provide location and orientation of transverse, anterior chamfer cuts to fit the femoral implant.
Using the surface matching or registration technique illustrated in FIG. 2, the shapes of a model of the bone surface 21, generated from a pre-operative image, are matched to surface data points identified during the first incision or during surgery. Intra-operative surface data points can be specified by direct contact with percutaneous probes, from within the surgical exposure using ultrasonic or direct-contact optical probes, or from fluoroscopic radiographic images. Location tracking is a critical step in CAS. Tracking devices are attached to a target bone and to any tools to be used during the operation, such as drills, reamers, guides, or screwdrivers. Many common tracking devices use optical cameras and infrared light emitting diodes. These optical sensors are easy to set up, very accurate, have fast sensing rates of up to 100 measurements per second, and can track multiple tools simultaneously. A disadvantage of the devices illustrated in FIGS. 1 and 2 is that they require additional surgical time, require a direct line of sight to perform the procedure, require special training of surgeon and staff, require maintenance and frequent calibration of the robotic mechanism(s), and can be very expensive, depending on the required level of accuracy.
Other tracking technologies use acoustic or magnetic sensors that create an electromagnetic field around the surgical site that is altered as instruments move within the field. Such devices do not require a direct line of sight, but the devices may be less accurate, cannot be used with metallic tools, and have difficulties tracking multiple tools simultaneously. One major benefit of either of these tracking methods is a reduction in radiation, due to elimination of the need for intra-operative fluoroscopy or radiography to check component position.
The systems described in the preceding discussion often suffer from a lack of readiness for the operating room and do not always address practical considerations. Many systems introduce additional capital equipment, equipment maintenance and operative steps into the surgical procedures that prolong the surgery and require significant training. Further, most of the systems do not address the issues of sterility and safety, and unwanted motion of the body part(s) to be operated upon. Most systems require input from the surgeon in order to specify data or alter program flow. Many systems rely on a non-sterile assistant to enter data, using a keyboard, mouse or pen, but this is inefficient and risks miscommunication. A sterilized or draped input device, introduced into the surgical operating theater, may be difficult to use, may be distracting for the surgeon, requires the splitting of the surgeon's attention between the display screen in one location and the surgical tool in another, and requires removal of the tool from the surgical site for use elsewhere as an input device.
What is needed is a system that requires only one surgical procedure (defined as requiring at least one incision or cutting operation), employs a pre-operative scanning procedure that provides micron level accuracy, is flexible enough to account for certain tolerances relative to an idealized fit, and provides a fabricated, patient-specific cutting jig and a patient-specific (optional) implant device whose components can be aligned and altered according to the body part(s) involved.